HP actually has no real relevance to cars, that use torque to move them.
Quite true.
Even simply using the peak hp number is surprisingly accurate performance potential indicator , where as looking at peak torque is a complete waste of time.
Peak torque is not a performance indicator.
Peak horsepower is not a performance indicator.
Best performance is given by maximizing the area under the torque curve from near the torque peak to near the power peak. Remember that for any torque value on the torque curve there exists a corresponding power value, they change together.
But average power is another beast.
HP = Mass x Distance / Time
if:
Mass = 3000 lbs
Distance = 1320 ft
Time = 12 sec, then:
HP = 3000lbs x 1320ft /12sec = 330,000 lbft/s = 600HP
Horsepower is a valid indicator of how much power is needed for a 3000lb car, to cover 1320 ft, in 12 s.
But it does not tell us anything about acceleration in each gear, shift points, traction limits or gear selection.
If we seek to learn about acceleration, traction limits, we work with torque.
If we are looking for maximum speed, we need engine rpm, gearing and tire size.
If we want to go really, really fast, we work with money.